The present invention relates to a device for filtering and separating especially biologic-organic flow media by reverse osmosis as well as by microfiltration, ultrafiltration, and nanofiltration with a pressure-tight housing having an inlet for the flow medium and outlets for the retentate as well as for the permeate. A plurality of spaced-apart filter elements are arranged within the housing which are in the form of a membrane cushion and along which the flow medium passes.
A device of the aforementioned kind is, for example, known from German Patent 37 15 183. In this known device the flow medium to be separated is introduced via an inlet of the device and passes in a controlled, regular pattern through the membrane cushions arranged between spacer elements so as to flow alternatingly from the exterior to the interior and from the interior to the exterior of the membrane cushion until it exits, after flowing past all of the membrane cushions, the device as an enriched retentate. The spacer elements are circular and the membrane cushions can also be of a circular design or, in approximation of a circular shape, may have the contour of a polygon.
With the known device very good results are achieved for certain applications such as salt water desalination, i.e., for producing potable water from salt water, whereby in the known device, even for large filter element stacks, the partial pressure differences of the flow medium between inlet and outlet remains within reasonable limits.
However, when flow media, for example, liquids with a high contents of biologic-organic and/or inorganic compounds must be separated, the rapid, disadvantageous formation of a filter cake can be observed, because the compounds contained in the flow medium will deposit on the membrane cushions, respectively, at locations of the spacer elements at which the flow velocities of the flow medium is lower than at other locations of the device or at projections that extend upwardly from the surface of the spacer elements. This results in the device losing its separating capacity so that the device must be demounted and, if necessary, cleaned in a very complicated manner. Such a procedure is disadvantageous and cannot be performed regularly because for many applications the device must function without requiring servicing, because an interruption of the operation of the device for cleaning, maintenance, and replacement purposes would result in unacceptable ecological and economical consequences.
It is therefore an object of the present invention to provide a device of the aforementioned kind which is able to separate liquids with a high biologic-organic and/or inorganic material contents whereby no deposits in form of filter cakes should result during operation. Furthermore, the device, if this should become necessary, should allow for simple cleaning and maintenance and should provide for an inexpensive and simple manufacture. It should also be adaptable to individual loading degrees of the liquids to be separated.